Does single or double quote matter in str_ireplace in PHP?

Question

I've to replace newline (\\n) with & in a string so that the received data could be parsed with parse_str() into array. The thing is that when I put \\n in single quote it somehow turns out as to be replaced with a space:

str_ireplace(array('&', '+', '\n'), array('', '', '&'), $response)
"id=1 name=name gender=gender age=age friends=friends"

But when I put \\n in double quotes then it works just fine:

str_ireplace(array('&', '+', "\n"), array('', '', '&'), $response)
"id=1&name=name&gender=gender&age=age&friends=friends"

Why is that so?

Answer 1

Because only the escaped sequences \\' and \\\\ have a meaning in single quoted strings.
See the documentation :

To specify a literal single quote, escape it with a backslash ( \\ ). To specify a literal backslash, double it ( \\\\ ). All other instances of backslash will be treated as a literal backslash: this means that the other escape sequences you might be used to, such as \\r or \\n , will be output literally as specified rather than having any special meaning.

Update:

Another difference is that PHP only substitutes variables inside double-quoted strings (and heredoc) . Therefore you can consider processing of single-quoted strings to be faster in general (but maybe not measurably faster).

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Btw you don't necessarily need to use str_ireplace as & , + and \\n have no upper or lower case version. There is just one version, so str_replace would be enough.